Reinforcing tape comprising a ply of longitudinal high-tenacity yarns

ABSTRACT

Reinforcing tape ( 1 ) that includes a ply ( 2 ) of longitudinal, aramid-, glass- or carbon-based high-tenacity yarns ( 3 ) bound together by weft yarns ( 4 ), which tape includes two thermoplastic films ( 5, 6 ), each placed on one side of the ply ( 2 ) of high-tenacity yarns ( 3 ).

FIELD OF THE INVENTION

[0001] The invention relates to the field of high-performance textiles,and more precisely to textile reinforcements used as reinforcingelements. It relates more particularly to a novel structure ofreinforcing tape produced from high-tenacity yarns that are used inorder to be wound around various structures for the purpose ofreinforcing them.

[0002] The aim of the invention is to improve this type of tape so as tobe able to preserve almost all of the tenacity properties of these tapeswhen they are subjected to high stresses, both mechanical stresses andthose from the standpoint of the environmental conditions.

PRIOR ART

[0003] In general, very many structures have to be reinforced since theyare the seat of particularly high mechanical stresses. As an example,mention may be made of flexible pipes used in the field of oil drilling,which have to withstand particularly high pressures when they areconducting pressurized gases. The stresses are not only mechanical, butalso thermal and chemical since the materials employed must be inertvis-a-vis the gases being transported and must not be degraded when theyare used in an aqueous and/or saline medium. This is why the pipes usedinclude textile reinforcements in the form of tapes wound in a helixaround the central portion of the pipe. To ensure that the pipe is wellable to withstand the internal pressure within the pipe, it is known touse tapes based on high-tenacity yarns, and especially aramid-basedyarns, glass fibers or carbon fibers.

[0004] Such a tape may in particular be produced using the teachings ofthe Applicant's document EP 0 193 478. This is because such a tapecomprises longitudinal aramid yarns bound together by loosely woven weftyarns in such a way that the aramid yarns have the least possibleshrinkage and are therefore flat in order to maintain their mechanicalproperties.

[0005] Various problems arise with the tapes produced from thesehigh-tenacity fibers and especially degradation in the mechanicalproperties of the tape due to the contact of this tape with the elementsthat surround it. Thus, several different tapes are often used, whichare wound around one another, generally in different directions. In thiscase, the aramid, glass or carbon yarns come into contact with oneanother and therefore rub against one another, especially when the pipeis flexible, since the various superposed layers have a tendency toslide over one another. This may result in the degradation of themechanical properties of some of the yarns, with the appearancetherefore of areas of weakness that may completely prejudice theintegrity of the pipe.

[0006] The longitudinal aramid, glass or carbon yarns may also come intoabrasive contact with the other reinforcing elements that are used in acomplementary manner. It will of course be appreciated that the use ofthe metal reinforcements, or more generally the use of a material ofhigh hardness, may cut certain fibers, thereby reducing, at leastlocally, the overall toughness of the tape. Furthermore, it may turn outthat the reinforcing tapes are covered with impermeabilizing materials,such as resins or other rubbery materials that are cured in situ. Inthis case, such materials at least partly penetrate inside the fibersand, after curing, preclude the possibility of the fibers of any oneyarn sliding relative to the others. This results in the stiffening ofthe tape, which limits the flexibility of the pipe and may even degradethe tenacity properties of the longitudinal yarns.

[0007] This drawback is observed in particular in tapes that haveundergone a step in which they is coated with a thermoplastic for thepurpose of protecting them from external attack.

[0008] Moreover, it is known that aramid fibers are very sensitive toultraviolet radiation. This is because prolonged exposure of the aramidyarns to sunshine results in degradation of the chemical structure ofthe aramid fibers, which results not only in a change in their color butabove all in their mechanical strength properties being degraded. Thisis why, when they are being transported, spools of aramid tape aregenerally protected by opaque packaging. However, this protection iseffective only while the tape is inside the packaging, and as soon asthe tape is employed, to be wound around the pipe or more generally itssupport, it is exposed to attack by ultraviolet radiation. In otherwords, the protection afforded by the opaque packing is not completelysatisfactory since it does not guarantee protection from ultravioletright up to when the tape is installed in the final application.

[0009] Furthermore, it may happen that the final application of thereinforcing tape means that the latter remains exposed to ultravioletradiation, and therefore its properties will degrade after it has beeninstalled. Mention may especially be made of the use of this tape as areinforcing element for civil engineering works, and especially bridgepiles. In this case, the tape is almost immersed in water which is alsoknown to degrade the mechanical properties of the aramid.

[0010] The problem that the invention aims to solve is that ofpreserving the mechanical properties of reinforcing tapes based onlongitudinal high-tenacity yarns, and to do so despite being exposed tothe external environment, especially moisture or ultraviolet radiation.Another problem is that of protecting this tape from the variousabrasive contacts when the tape is being installed.

SUMMARY OF THE INVENTION

[0011] The invention therefore relates to a reinforcing tape thatincludes, in a known manner, a ply of longitudinal, aramid-, glass- orcarbon-based high-tenacity yarns bound together by weft yarns.

[0012] According to the invention, this tape is characterized in that italso includes two thermoplastic films, each placed on one side of theply of longitudinal yarns.

[0013] Put another way, the invention consists in covering both sides ofthe ply of longitudinal yarns with a layer of thermoplastic, which doesnot penetrate into the ply, and therefore lets the inner fibers of theyarns have a freedom of movement. These thermoplastic films thereforeprovide mechanical protection for the yarns from external contacts, andwithout binding the fibers together, thereby leaving the tape theability of undergoing sufficient deformation in order to be able to beconfigured according to the geometry of the article to be reinforced,and maintaining high mechanical properties. These thermoplastic filmsare therefore interposed between the plies of yarns of different tapeswhen these are superposed, therefore preventing direct contact betweenthe yarns and therefore preserving them from a certain amount ofabrasion.

[0014] In practice, the thermoplastic films may adhere slightly to thatside of the ply which they cover, in such a way that they then have thesame width as that of the ply.

[0015] In an alternative embodiment, the two thermoplastic films may bebonded together along the edges of the tape, and therefore in this wayimprison the ply of yarns. These films may result either from twoseparate sheets welded together along the two edges of the tape, or elsefrom a single sheet folded over itself, being welded along only one edgeof the tape.

[0016] Advantageously in practice, the ply of longitudinal yarns may becapable of sliding within the sheath formed by the two films. In otherwords, the ply of yarns has a certain degree of freedom relative to thefilms that do not adhere to the ply, but on the contrary allow it tomove slightly. This freedom of movement of the ply allows the latter tomove when the movement is configured or wound onto its application, insuch a way that the stresses on the high-tenacity yarns are relativelydistributed, which is conducive to mechanical properties beingmaintained.

[0017] In a preferred form, applied in the aramid case, to the films hasultraviolet radiation blocking properties so that the aramid yarns ofthe tape are protected from external radiation and therefore retaintheir initial mechanical properties. Thus, the aramid fibers areprotected as soon as the tape has been produced, by placing it incharacteristic films, right up to the end use on the article to bereinforced.

[0018] Advantageously in practice, the longitudinal yarns may be boundtogether by at least partly thermoplastic weft yarns. These weft yarnsmay either be based on a thermoplastic or may be yarns having a core andcoatings of a thermoplastic. It is also possible to use weft schemescomprising one or more weft yarns per step.

[0019] Thus, it may be advantageous to use, both for the weft yarns andfor the films covering the ply, thermoplastics having similarproperties, especially as regards softening temperatures, so that, wheninstalling the characteristic films, a heating operation is carried outwhich reveals the thermoplastic properties of the weft yarns, thusanchoring the films on the weft yarns.

[0020] In practice, in order to provide protection from moisture, it isalso possible to use microporous films that have breathing properties,and therefore allowing a moisture present inside the external sheathformed by the film to be removed.

BRIEF DESCRIPTION OF THE FIGURES

[0021] The manner in which the invention is realized, and the advantagesthat stem therefrom, will become clearly apparent from the descriptionof the embodiments that follow, supported by the appended figures, inwhich:

[0022]FIG. 1 is a top view of a tape according to the invention, inwhich a portion of one of the characteristic films has been removed;

[0023]FIG. 2 is a cross-sectional view of the tape shown in FIG. 1; and

[0024]FIGS. 3 and 4 are sectional views of alternative embodiments.

MANNER OF REALIZING THE INVENTION

[0025] The tape (1) illustrated in FIG. 1 comprises a ply (2) of aramidyarns (3) woven loosely with weft yarns (4). This ply (2) receives, oneach of its sides, a thermoplastic film (5, 6).

[0026] In the embodiment illustrated in FIG. 1, the two films (5, 6) arewider than the ply of yarns (3) and extend laterally therefrom inregions in which they face each other where they will be weldedtogether. These welding regions therefore form the edges (8) of thetape.

[0027] In this way, the sheath formed by the two films (5, 6) allows theply (2) of yarn to move slightly and facilitates its deformation whenthis tape is used on supports that are not flat.

[0028]FIG. 3 illustrates an alternative embodiment in which the sheathis formed by a single film (19) folded over on itself in order to formthe edge (11), which sheath is welded to itself in the region (12)corresponding to the edges of the sheet forming the film (10).

[0029] The invention also covers the embodiment illustrated in FIG. 4,in which the ply (2) of aramid yarns receives two separate films (15,16), each on one side of the ply (2). In this case, the two films (15,16) adhere slightly to the ply of aramid yarns, after they have beenexposed to a heat source.

[0030] In practice, the yarns (3) of the ply (2) are aramid-based andtherefore may in particular be chosen from the products sold under thebrand name KEVLAR® by DuPont or TWARON® by Teijin. Each yarn maypreferably be a multi-end cabled yarn, of unitary linear density between1670 dtex and 3300 dtex, depending on the function of the applications.The yarn may also receive a twist in the S and Z directions of about 60turns/meter. Of course, the number of ends, and the linear density ofeach end and their twist, may be adapted according to the desiredapplication.

[0031] In practice, good results are obtained when using plies whoseyarns, possibly multi-filament yarns, are numerous, about ten percentimeter and over a width that may range from about five to twentycentimeters.

[0032] As already mentioned, the ply (2) of aramid yarns is wovenloosely, that is to say in such a way that the warp yarns are as flat aspossible, and therefore have a particularly low shrinkage. This type ofweaving, also called “high-modulus weaving”, therefore means that theshrinkage of the weft yarns is relatively high. The weft yarns aretherefore relatively spaced apart, typically by around one to threeyarns/centimeter approximately.

[0033] The yarn employed to form the weft (4) preferably hasthermoplastic properties. It may, for example, be a polyester yarn,typically with a linear density from 4.9 to 110 tex. It may also be ayarn having a core, which is not thermoplastic, for example based onglass fibers with a linear density of 5.5 to 68 tex, having a sheath,which is thermoplastic, for example based on polyamide.

[0034] Good results have been obtained by using polyester based films(5, 6) having a thickness of around 20 to 50 microns. This polyesterfilm has the advantage of being thermoplastic, but the invention alsocovers other variants in which the film has specific properties. Forexample, it is possible to use multilayer complex films having, forexample, a coating with a low friction coefficient, such as apolytetrafluoroethylene coating. It is also possible to use filmspossessing breathable properties, chosen to allow water vapor to passfrom inside the sheath to the outside, while preventing water frompenetrating into the sheath when the latter is immersed. It is alsopossible to use films having fillers that make the film opaque tocertain types of radiation, especially ultraviolet radiation, the latterbeing known to cause degradation of the mechanical properties of thearamid.

[0035] In practice, the tapes thus obtained have a strength of the orderof a few tens of kN/cm of width, the useful width being measured only onthe ply of aramid yarns.

[0036] In practice, the tape according to the invention may be obtainedby installing the characteristic films on a ply of aramid yarns,however, it will generally be preferable for the characteristic films tobe installed directly after the weaving operations. Thus, as the ply (2)comes off the loom, it receives, on its top and bottom sides, theplastic films (5) and (6) which may be heated differently, andespecially by exposure to radiation from a heat source. This heatingraises the temperature of the films (5, 6) and a very slight melting oftheir surface in contact with the aramid ply (2) therefore causesadhesion.

[0037] This exposure to a heat source not only causes slight melting ofthe characteristic films, but also that of the weft yarns (4) that linkthe aramid yarns (3). These weft yarns thus adhere to the aramid yarns,thereby improving the integrity of the ply, although the number of weftyarns is particularly small.

[0038] This operating method is used in particular to produce the tapeillustrated in FIG. 4. The combination of ply (4) and films (15, 16) maythen be subjected to a slight pressure, making the adhesion uniform.This pressure may be obtained by calendering, but it may also resultfrom the intrinsic pressure when winding the tape on a mandrel.

[0039] To produce the tape (1) shown in FIGS. 1 and 2, the films (5) and(6) are also placed above and below the ply (4) of yarns, and optionallyheated. They then receive, by heated rollers located along their edge,the amount of heat for producing the welded region (7).

[0040] Of course, the invention is not limited to merely the embodimentsillustrated in the figures and specified by numerical values, ratherthey may cover many alternative embodiments chosen according to theapplications, especially when the high-tenacity yarns are glass orcarbon yarns.

[0041] It is apparent from the foregoing that the tape according to theinvention has many advantages, especially that of allowing the aramidyarns to be protected from ultraviolet radiation and from other externalfactors, especially moisture. It also provides mechanical protection ofthe high-tenacity fibers from the abrasion generated by contact withother mechanical elements, and especially with the tape itself when thelatter is wound. This protection is provided without degrading themechanical properties of the yarns employed.

1. A reinforcing tape (1) that includes a ply (2) of longitudinal,aramid-, glass- or carbon-based high-tenacity yarns (3) bound togetherby weft yarns (4), which tape includes two thermoplastic films (5, 6),each placed on one side of the ply (2) of high-tenacity yarns (3). 2.The reinforcing tape (1) as claimed in claim 1, wherein eachthermoplastic film (15, 16) adheres to one side of the ply (2).
 3. Thereinforcing tape (1) as claimed in claim 1, wherein the twothermoplastic films (5, 6) are bonded together along the edges (8) ofthe tape (1).
 4. The reinforcing tape (1) as claimed in claim 3, whereinthe ply of longitudinal yarns is capable of sliding inside the sheathformed by the two thermoplastic films (5, 6).
 5. The reinforcing tape(1) as claimed in claim 1, wherein each film (5, 6; 10; 15, 16) hasultraviolet radiation blocking properties.
 6. The reinforcing tape (1)as claimed in claim 2, wherein the longitudinal yarns are bound togetherby at least partly thermoplastic weft yarns.
 7. The reinforcing tape (1)as claimed in claim 6, wherein the thermoplastic of the weft yarns andthe material of the films covering the ply (2) are similar.